Intervertebral discs stabilize the spine and distribute forces between consecutive vertebrae. A healthy disc has two parts. First, there is an inner gelatinous nucleus pulposus. Second, there is an annulus fibrosis that surrounds, and in healthy discs, confines the nucleus pulposus.
Due to trauma, disease or aging, intervertebral discs may become damaged or displaced. For example, in some circumstances, disruption of the annulus fibrosis may allow the nucleus pulposus to protrude into a vertebral canal. This type of displacement and damage is commonly referred to as a herniated or ruptured disc, and when it occurs, the extended nucleus pulposus may press on a spinal nerve. This pressure may cause pain, numbness, nerve damage, muscle weakness and paralysis. Also, disruption of the annulus fibrosis can allow the leakage of inflammatory cytokines causing irritation and pain of surrounding nerve structures.
In other circumstances, discs deteriorate due to the normal aging process. As a disc dehydrates, the disc space height may be reduced, leading to instability of the spine, compression of nerve structures and pain.
Spinal disc pain and diseases associated with the spine may be treated by one more strategies, including but not limited to surgery physical therapy and the administration of medication.
Surgery can be an effective means by which to correct some underlying problems such as disc herniation through removal or reorientation of problematic tissue. However, surgery can be expensive, time consuming and uncomfortable. Moreover, not all patients are candidates for surgery, and surgery is not necessarily effective at treating all causes or symptoms of pain or disease.
Physical therapy alone or in combination with surgery can also be effective to treat or to alleviate some of the pain associated with different spinal conditions. However, physical therapy can be a long process and as with surgery not all patients are candidates for physical therapy.
Because neither surgery nor physical therapy alone or in combination is sufficient to treat all forms of disc disease and pain, it is important to develop better ways to administer medication to address these types of disease and pain. The current standard of care for administering medications to the back and spine is to administer biologic therapies that involve single injections of a drug solution into a disc. Unfortunately, these drug solutions are not retained in the disc for sufficient periods of time and often the drug solution remains effective only in or around the area that it treats.